For the convenient, inexpensive and rapid self-service of food to the public under open room conditions there are many critical considerations involved including protecting food against contamination yet providing full selectivity and quick accessibility.
Conventional sliding or pivoted access doors with windows provide some environmental protection for food displayed under room conditions but slows the movement of patrons if kept closed as they should be between servings.
Spring or gravity closed sliding or pivoted access doors with windows provide some environmental protection for the food displayed but slows the progress of patrons and increases spillage and clean-up requirements caused by collisions with the moving closures. Wide open spaces above or in front of a shelf for access to the food permits foreign particles in the circulating air to contaminate the food while any protective positive air movement provided to prevent this dries the food and may interfere with shelf replenishment.